This invention relates to an image forming apparatus such as a printer, a facsimile or a copier, and particularly relates to an image forming apparatus having a sheet feeding device capable of continuously feeding printing sheets.
In order to feed printing sheets at constant intervals, a conventional image forming apparatus has a sheet sensor on a sheet feeding path from a sheet storing portion to a photosensitive drum. A separating member lifts a trailing end of a preceding sheet so that the trailing end moves out of a detectable area of the sheet sensor, while the sheet sensor is used to position a leading end of a subsequent printing sheet. After the positioning of the leading end of the subsequent printing sheet is completed, the separating member moves the trailing end of the preceding sheet downward, so that a constant spatial interval is formed between the preceding sheet and the subsequent sheet. An example of such an image forming apparatus is disclosed in Japanese Laid-Open Patent Publication No. 5-193782 (in particular, Page 1 and FIG. 1).
However, in the above described image forming apparatus, it is necessary that the printing sheet warps with a suitable balance when the separating member lifts the printing sheet. Thus, the separating member needs to have a member that acts on the printing sheet uniformly throughout the width of the printing sheet, and therefore the size of the sheet feeding device may increase. Moreover, it is necessary to control the movement of the separating member in addition to a general sheet feeding device, and therefore the controlling of the sheet feeding device may become complicated.